Teams from a dozen nations have been searching by air and sea for the ARA San Juan, which has 44 crew aboard and was last contacted off the coast of Argentina on November 15.

The latest update comes as the clock runs down on the chances of finding the vessel before its air supply runs out.

The San Juan has enough air to last seven to 10 days if it has remained fully immersed since that time, experts say. If the submarine has surfaced or “snorkeled” — that is, raised a tube to the surface to refresh the vessel’s air — since then, the crew may have bought more time.

Anxious families have been waiting at Argentina’s Mar del Plata navy base, to which the submarine was heading when it vanished, for news of their loved ones. Meanwhile, ships and aircraft are scouring a swath of the South Atlantic for the missing vessel.

Argentinian officials on Thursday briefed relatives of the crew members about the explosion. Overcome with grief, family members gathered at the navy base sobbed and held each other up.

Balbi said information about the noise had first been given to Argentina on Wednesday by the United States.

In addition, the Comprehensive Nuclear Test-Ban Treaty Organization, or CTBTO, based in Vienna, Austria, informed Argentina on Thursday that its monitoring systems had detected an unusual sound.

On November 15, it said, “two CTBTO hydroacoustic stations detected an unusual signal in the vicinity of the last known position of missing Argentine submarine ARA San Juan.”

The sound of “an underwater impulsive event” was detected at 1:51 p.m. GMT (10:51 a.m. local time) by its underwater microphones, it said. The organization is set up to monitor compliance with the proposed nuclear test ban treaty and has 11 hydroacoustic stations positioned around the world listening for signs of nuclear explosions.

“Details and data are being made available to the Argentinian authorities to support the search operations that are underway,” the organization said.

Balbi said six teams were currently searching for the missing submarine in waters of the Gulf of San Jorge, about 430 kilometers (268 miles) from the coast. The depth of the ocean varies considerably there, ranging from 200 to 2,000 meters, he said.

There was no evidence of any attack and no information on the cause of the noise, Balbi said.

‘Critical phase’ of search

Balbi said in a Wednesday news conference that there had been “no type of contact, not passive nor active,” with the submarine since November 15 and that the search was “in the critical phase.”

A spokesman for the UK Ministry of Defense confirmed Thursday that a Royal Air Force C-130 aircraft had landed in Argentina and was now a part of the search, as was a Voyager, a refueling aircraft that helps searches go on longer.

It appears to be the first time since the Falklands conflict in 1982 that an RAF plane has landed in Argentina, although the UK Ministry of Defense would only characterize it as the first time in a “very long time.” The Royal Navy’s ice-patrol ship, HMS Protector, had already joined the search.

Russia has also sent navy specialists and equipment to Argentina, state news agency Tass cited the Russian Defense Ministry as saying Thursday. The deployment includes a ship equipped with two deep-water vehicles capable of searching depths of up to 6,000 meters.

The US Navy has sent underwater search vehicles and two undersea rescue systems that could be used to rescue crew members.

The Argentine navy lost contact with the San Juan shortly after the vessel’s captain reported a failure in the battery system while the sub was submerged off Argentina’s South Atlantic coast, the military said.

The submarine was traveling from a base in Argentina’s far southern Tierra del Fuego archipelago to its home base in Mar del Plata on the northern side of the country.

Families’ tense wait for news

Federico Ibáñez, whose brother Cristian is a radar technician on the San Juan, was among the family members and well-wishers gathered outside the Mar del Plata navy base on Wednesday.

Speaking to CNN before news of the possible explosion emerged, he questioned why the Argentine navy continued to say the submarine could be on the ocean surface, and why rescuers took so long to begin searching the ocean floor.

“It’s a lack of respect,” said the 34-year-old. “If it was on the surface, they would have found it. They didn’t, and they didn’t look for them at the bottom. If they did it earlier, it could have been different.”

He fears the situation will end badly. “They keep saying that a submarine in good condition can have this much time, but they don’t say how long they have if the submarine is not in good condition. So, what if it’s in bad shape?”

Cristian Ibáñez has a daughter, Elisa, 9. His wife, Fernanda Valacco, has told the girl little, hoping that her husband will return and she won’t have to explain what happened.

“She knows her father is missing, but she knows he’s fine and will be home soon,” Valacco said on Wednesday. “I am sure all of the 44 will be fine and could come here any moment.”

Federico Ibáñez described a tense atmosphere on the navy base as family members huddled together praying for word of the sub’s discovery.

“They all stay there in a big room with bunk beds and some desks. Everybody is silent. Everybody is waiting. Waiting for what? I cannot stay there,” he said.

Also aboard the sub is Eliana Maria Krawczyk, Argentina’s first female submarine officer.

In 2004, she joined the navy after seeing an advertisement about military ships. She has voiced hopes of one day commanding a sub herself.

“At the time, there weren’t any female officers in the force. I took it as a challenge,” she once told the Argentine Defense Ministry in a video interview. “You can do the same things that any men do, even if you are in a traditionally male-dominated environment. … Any women can do it.”